Wavemeter



Aug. 26, 1958 Filed Nov. 3. 1954 D. R. DE TAR WAVEMETER 2 Sheets-Sheet 2Filed Nov. 3, 1954 Ezel-:ZEE DONALD Q. DETAR WAVEMETER Donald R. De Tar,Stratford, Coun., assigner to Aladdin Industries, Incorporated,Nashville, Tenn., a corporation of Illinois Application November 3,1954, Serial No. 466,508 s claims. (Cl. ssa-s2) One principal object ofthe invention is to provide an improved wavemeter or the like for use atultrahigh frequencies, particularly in the ultrahigh frequency (U. H.F.) television band extending from 470 to 890 megacycles.

A further object of the invention is to provide an absorption typewavemeter which is inexpensive and small in size, yet is accurate andentirely reliable.

It is another object of the invention to provide an improved wavemeterwhich is simple and rugged in construction, easy to use and convenientto carry.

Further objects and advantages of the invention will appear from thefollowing description, taken with the accompanying drawings, in which:

Figure l is an elevational view of an exemplary wavemeter constitutingan illustrative embodiment of the invention;

' Fig. 2a is a fragmentary double-size longitudinal sectional view takengenerally along fa line 2 2 in Fig. 1;

Fig. 2b is a continuation of Fig. 2a showing the opposite end of thewavemeter;

Figs. 3, 4, and 5 are cross-sectional views taken generally along lines3 3, 4 4, and 5 5 in Figs. 2a1 and 2b;

Figs. 6 and 7 are plan and elevational'views of an inductance elementembodied in the wavemeter of Fig. 1;

Fig. 8 is a diagrammatic representation of the wavemeter; and

Fig. 9 is an approximate equivalent schematic diagram of the wavemeter.

Considered in greater detail, the drawings will be seen to illustrate anexemplary wavemeter 10 which in this instance comprises an elongatedcylindrical tubular housing 11 made of a dielectric material. One end ofthe housing 11, shown at the left in Figs. l and 2a, is closed by a dustcap 12.

To provide an inductance loop, a conductive metallic sleeve 13 ismounted within the left hand end of the insulating housing 11 and inthis instance is suitably secured to the housing 11 as by theillustrated screw 14. In order that the sleeve may define an inductanceloop, a pair of diametrically opposite longitudinal slots 15 are formedin the right hand end portion of the sleeve 13. As shown to best`advantage in Fig. 6, which is a view of the inductance element 13, theslots 15' extend part way from the right hand end of the element 13toward its left hand end. By virtue of the slots 15, the sleeve 13constitutes a generally U-shaped inductance loop having a pair ofelongated arms 16 which are interconnected at their left hand ends by aring-shaped portion 17 of the sleeve 13. Adjacent the ring portion 17the arms 16 have narrowed down portions 18 which are defined by cutouts19 in the sleeve 13. Adjacent the right hand end of the sleeve 13, thearms 16 are provided with externally reduced portions 20 having terminalelements 21 which are reduced in width by cutouts 22. Internally, thesleeve 13 is formed with a continuous cylindricalsurface 23.

United. States Patent O 2,849,691y Patented Aug. 26, 1958 ICC In orderto vary the capacitance between the arms 16 of the inductance loopdefined by the sleeve 13, the wavemeter 10 is provided in this instancewith a capacitive tuning member, indicated generally by the character24. While the member 24 may assume various forms, it is illustrated ascomprising inner and outer concentric cylindrical elements or sleeves 25and 26 in capacitive relation to the arms 16 of the stationary sleeve13. In this instance, the arms 16 are telescopically disposed betweenthe sleeves 25 and 26. The sleeve 26 is adapted to be received over theexternally reduced portions 20 of the arms 16, while the inner sleeve 25is adapted to be received within the internal cylindrical surface 23.Thin walled insulating bushings 27 and 28 are interposed between thestationary sleeve 13 and the inner and outer capacitive tuning sleeves25 and 26. It will be seen that the inner tuning sleeve 25 is relativelylong, while the outer sleeve 26 is relatively short. In the illustratedconstruction, the outer sleeve 26 is mounted on and conductivelyconnected to the right hand end of the inner sleeve 25. Morespecifically, the outer sleeve 26 is formed with an internally reducedor necked-down right hand portion 29 which is mounted on an externallyreduced end portion 30 of the inner sleeve 25. The connection betweenthe sleeves 25 and 26 is primarily for mechanical rather than electricalreasons, and hence need not be conductive. Both sleeves 25 and 26 are atsubstantially the same electrical potential, amounting to the meanbetween the potentials of the arms or terminals 16 of the inductanceelement 13. Accordingly, no substantial current flows between thesleeves 25 and 26.

Provision is made for effecting relative longitudinal movement betweenthe inductance element 13 and the capacitive tuning element 24. In thisway, the capacitance between the arms 16 may be varied so as to changethe resonant frequency of the inductance loop delined by the element 13.In this instance, the capacitive tuning element 24 is movable relativeto the housing 11, while the element 13 is stationary, but it will beunderstood that this arrangement might well be reversed. In theillustrated construction, the inner sleeve 25 of the capacitive tuningelement 24 is connected to the left hand end of an insulating rod 31,which is received within an axial bore 32 formed in the sleeve 25 and ispinned or otherwise suitably secured to the sleeves 25 and 26. The rod31 extends axially within the housing 11 toward its right hand end. Inorder to advance and retract the rod 31, its right hand end is connectedto a micrometer lead screw 33 which in this instance is provided with aquintuple left hand thread. The screw 33 is in threaded engagement witha nut 34 fixed in the right hand end of the housing 11. To reducefriction and wear, the

screw 33 is preferably made of metal, while the nut 34 is made of nylonor other similar plastic. For the purpose of preventing play or backlashbetween the screw 33 and the nut 34, the latter is formed with anexternally reduced or necked-down portion 35 which is longitudinallysplit by diametrically opposite slots 36. A split circular wire springor C-ring 37 is mounted on the outside of the reduced portion 45 tocompress the split halves of the nut 34 into intimate engagement withthe screw 33.

To provide for manual adjustment of the wavemeter 10, a generallycylindrical thimble-shaped dial or barrel 38 is mounted on the righthand end of the lead screw 33. In the illustrated construction, the leadscrew is formed with a reduced end portion 39 received within a bore 40in the dial 38. A setscrew 41 or some other fastening element isemployed to secure the dial 38 to the lead screw 33. The dial 38 isprovided with a tubular left hand portion 42 which is telescopicallyreceived over the housing 11 and thus is effective to enclose the screw33 and the nut 34. Asuitable scale 43 may be applied to the outside ofthe dial 38. It will be understood that the scale 43 may be calibratedin terms of frequency or wave length. In this instance the scale 43 ishelical in form. A pointer 44 is mounted on the housing 11 to cooperatewith the indicia on the scale 43. Due to the helical lead of the scale43, the pointer 44 remains opposite the scale as the dial is rotated toadvance the screw 33.

In operation, the inductive element 13 of the wavemeter is coupled to aresonant circuit or other element, the operating, frequency of which isto be determined. This is done by holding the wavemeter 10 with itslefthand end adjacent the coil or other inductive element of theresonant circuit. In this way, the slotted sleeve 13 is positioned inthe magnetic field of the coilv under test. The dial 38 isthen adjusteduntil thewavemeter absorbs the maximum amount of energy from the circuitunder test. The absorbtion of energy may be indicated in various ways,as will be understood by those skilled in the art. For example, ifV thedevice under test is an oscillator utilizing an electronic dischargedevice, the absorption of energy by the wavemeter may be manifested bythe complete cessation of oscillations in the oscillator, or by avariation in the current to the grid or other electrode of the electrondischarge device. In the typical oscillator, the grid current will dropwhen energy is absorbed from the oscillator by the wavemeter. It will beunderstood that the grid current may be measured by means of asuitablemilliameter or the like. It will also be understood thatrotation of the dial 38 advances the screw 33 through the split nut 34and thereby moves the sleeves 25 and 26 in a longitudinal directionrelative to the sleeve 13. Accordingly, the

extent of telescopic engagement between the sleeve 13 and the sleeves 25and 26 will be varied. The greater the extent of telescopic engagement,the greater will be the capacitance between the arms 16 of theinductance loop defined by the sleeve 13. It will be understood that theinductance provided by the slotted sleeve 13 is resonated by thecapacitance between the arms 16. Accordingly, theresonant frequency ofthe wavemeter is varied by shifting the sleeves 25 and'26 longitudinallyrelative to the sleeve 13. The resonant frequency decreasesprogressively as the movable sleeves 25 and 26` are shifted intotelescopic relation with. the stationary sleeve 13.

The tuning curve of the wavemeter is affected by the configuration ofthe sleeve 13 and the length of the sleeves 25 and 26. In theillustrated construction, the inner sleeve 25 is relatively long, withthe result that it contributes capacitance betweenV the arms 16throughoutv the tuning range of the wavemeter. It will be understoodthat the capacitance afforded by the inner sleeve 25 increasesprogressively as the sleeve is moved into the slotted sleeve 13.Theouter sleeve 26, being relatively short in this instance, comes intoplay primarily in the low frequency portion of the tuning range, as thesleeve 26 moves over the ends of the arms 16. The reduced width of theterminal portions 21 of the sleeve 13 affords a band-spreading' effect,particularly at the high frequency end of the tuning range.

In Fig. 9 the inductance of the wavemeter, provided primarily by theslotted sleeve 13, is indicated by a lumped inductance -coil 45, whilethe capacitances between the respective arms 16 and the capacitivetuning element 24 are represented by first and second variablecapacitors 46 and 47-` connected in series across the coil 45. Thisapproximately equivalent schematic representation of the wavemeterillustrates the point that the capacitances between the armsl 16 and thesleeves 25 and 26 are in series. Fig. 8 illustrates diagrammatically thecapacitive relation between thecapacitive tuning element 24and the arms16 of the U-shaped loop defined by the sleeve 13.

Inview of the small size of the tuned circuit provided 4V by the slottedsleeve 13 and the tuning sleeves 2S and 26, the wavemeter 10 may beemployed effectively in cramped situations. Thus, the left hand or probeend of the wavemeter may bel inserted into an extremely small openingand thus may be coupled closely to a coil or other tuned element whichis relatively inaccessible. The tuned circuit of the wavemeter may becoupled to a circuit element of small size without being affectedappreciably by electromagnetic fields or other adjacent elements. Thisis a matter of particular advantage in testing television tuners, inwhich the coils or other tuned elements are often small in size andclosely spaced. Because of the length of the wavemeter, the left hand orprobe end may be inserted into a deep opening to secure close couplingbetween a circuit under test and the tuned circuit of the wavemeter,while leaving the right hand or adjustment end of the wavemeter in aconveniently accessible position for easy operation. The wavemeter maylbe made any desired length simply *by elongating the housingll and theinsulating rod 31.

The helical form of the scale on the wavemeter dial provides great scalelength in a small space. Since the pointer is stationary, while thescale is movable, the wavemeter may be read from a xed angle.Accordingly, readings may be taken without moving the probe end of thewavemeter from the position of optimum coupling with the circuit undertest.

By virtue of the stepped configuration of the slotted sleeve 13 and thedifference in length of the inner and outer sleeves 25 and 26, thefrequency scale or curve of the wavemeter may be made substantiallylinear. It will be recalled that theouter lsleeve 26 is effectiveprimarily at the low frequency end of the tuning range, while thereduced terminal ends 21 of the arm electrodes 16 provide band-spreadingat the upper end of the tuning.

range. The capacitive relation between the movable sleeves 25 and 26 andthe arms 16 eliminates any needk field from the coil will linkv thesingle turn loop provided' by the sleeve 13. The wavemeter may becapacitively coupled to a circuit under test by placing one of thearmelectrodes 16 adjacent acircuit element charged with a radiofraquency voltage.

Since the nut 34 preferably is made of an insulating material, there is.no possibility that electrical noise will be introduced by slidingengagement between the nut and' the screw 33. The springfloading of thesplit nut eliminatesv all backlash between the nut and the screw.

It will be observed that the dial or thimble 38 is provided with a largeknob portion 48 for making a fine adjustment of the dial, together witha smaller, axially protruding knob 49` for spinning the dial when a morerapid adjustment is desired.

The wavemeter is small in size and light in weight and, accordingly, iseasy to use and convenient to carry. Because of the simple, ruggedconstruction of the wave meter, there is little to get out ofadjustment. Moreover, the wavemeter may be manufactured inexpensively.

Various modifications, alternative constructions and equivalents may beemployed without departing from the true spirit and scope of theinvention as exemplified in the foregoing description and defined in thefollowing claims.

I claim:

1. An absorption type wavemeter, comprising an insulating elongatedtubular generally cylindrical housing, an inductance element in the formof a conductive sleeve received within said housing adjacent one endthereof, said sleeve having .a pair of diametrically oppositelongitudinal slots formed therein and extendinglongitudinally therealongpart way from the end sleeve remote from said one end of said housingtoward the end of said sleeve adjacent said one end of said housing,said slots defining a pair of opposed arm portions and aninterconnecting ring portion extending between said arm portions at theend of said sleeve adjacent said one end of said housing, outer andinner movable tuning sleeves disposed in said housing, said arm portionsof said rst mentioned sleeve having reduced terminal elementstelescopically received between said outer and inner sleeves, said ringportion being free of said tuning sleeves, an outer insulating bushingdisposed between said outer sleeve and said reduced terminal elements,an inner insulating bushing disposed between said inner movable sleeveand said rst mentioned sleeve, said outer and inner sleeves beingconductively interconnected, and means for longitudinally moving saidouter and inner sleeves to vary the extent to which said arm portionsare received between said tuning sleeves and thereby vary thecapacitances between said outer and inner sleeves and said arm portions,said means including an insulating rod connected to said movable sleevesand extending axially therefrom within said housing toward the endthereof opposite from said one end, a lead screw connected to theopposite end of said rod, a nut connected to said opposite end of saidhousing and in threaded engagement with said lead screw, a generallycylindrical dial telescoped over said opposite end of said housing andconnected to said lead screw, said dial being manually rotatable toshift said movable sleeves, and a pointer element mounted on saidhousing and in indicating relation to said dial.

2. An absorption type wavemeter, comprising an insulating tubularhousing, a U-shaped inductance element in the form of a conductivesleeve received within said housing adjacent one end thereof, saidsleeve having a pair of diametrically opposite longitudinal slots formedin one end thereof and defining a pair of opposed arm portions on saidsleeve and interconnected at one end by a bridge portion, interconnectedouter and inner movable cylindrical tuning elements disposed in saidhousing, said arm portions being telescopically received between saidouter and inner elements, said elements being free of said bridgeportion, outer and inner insulating bushings disposed between said armportions and said outer and inner elements, and means for longitudinallymoving said outer and inner elements to vary the extent of telescopingbetween said cylindrical elements and said arm portions and thereby varythe capacitance between saidarm portions, said means including a leadscrew connected to said elements, a nut connected to said housing and inthreaded engagement with said lead screw, a generally cylindrical dialtelescoped over said housing and connected to said lead screw, said dialbeing manually rotatable to shift said movable elements, and a pointerelement on said housing and in indicating relation to said dial.

3. An absorption type wavemeter, comprising an insulating elongatedtubular generally cylindrical housing, an inductance element in the formof a conductive sleeve received within said housing adjacent one endthereof, said sleeve having a pair of diametrically oppositelongitudinal slots` formed therein and extending longitudinallytherealong part way from the end of said sleeve remote from said oneendof said housing toward the end of said sleeve adjacent said one endof said housing, said slots defining a pair of opposed arm portions onsaid sleeve and an interconnecting bridge portion extending between saidarm portions, outer and inner movable tuning sleeves disposed in saidhousing, said arm portions being telescopically received between saidouter and inner sleeves, said tuning sleeves being free of said bridgeportion, an outer insulating bushing disposed between said outer sleeveand said arm portions, an inner insulating bushing disposed between saidinner movable sleeve and said arm portions, and means for longitudinallymoving said outer and inner sleeves to vary the capacitances betweensaid outer and inner sleeves and said arm portions, said means includingan insulating rod connected to said movable sleeves and extendingaxially therefrom within said housing toward the end thereof oppositefrom said one end, a lead screw connected to the opposite end of saidrod, a nut connected to said opposite end of said housing and inthreaded engagement with said lead screw, a generally cylindrical dialtelescoped over said opposite end of said housing and connected to saidlead screw, said dial being manually rotatable to shift said movablesleeves, and a pointer element mounted on said housing and in indicatingrelation to said dial.

References Cited in the file of this patent UNITED STATES PATENTS2,575,199 Stutt Nov. 13, 1951 2,606,315 De Tar Aug. 5, 1952 2,681,999Boothby June 22, 1954 2,710,379 Lubben et al. June 7, 1955

